1. Field of the Invention
The present invention involves novel vehicles for introducing one or more compounds of the oxime family into starting mixtures which can be utilized in the manufacture of coating materials.
2. Description of Related Art
The present invention relates to a concentrated solution of an anti-skinning agent in a suitable solvent. Anti-skinning agents are compounds that may be added to oil based coating materials, such as paints, stains and lacquers, to prevent the formation of skin or lumpy matter on the coating material as a result of oxidation during transportation or storage.
Compounds which have been used successfully as anti-skinning agents include phenols, substituted phenols, hydroquinones, polyphenols, dioxo-compounds, tin compounds, aliphatic amines and their salts, mixtures of organic hydroxylamines and β-dicarbonyl compounds or their derivatives, natural antioxidants such as (DL-α-tocopherol), and oximes. Oximes such as methyl ethyl ketoxime and butyl aldoxime have been particularly well received by the coating materials industry. These two widely accepted oximes compounds are liquids at room temperature and exhibit relatively high flash point temperatures. When these oxime compounds are employed as ant-skinning agents, they are typically utilized in essentially pure form.
While methyl ethyl oxime and butyl aldoxime are widely employed by industry, these particular oximes reportedly exhibit some degree of toxicity to humans. It appears likely that future use of these oximes will be regulated in various countries in order to protect public health. For example, the European Chemical Agency (ECHA) has announced its intention to restrict the future use of methyl ethyl oxime and butyl aldoxime in Europe under Regulation (EC) No. 1907/2006 concerning the Registration, Evaluation, Authorization and Registration of Chemicals (REACH). As another example, the Danish Environmental protection Agency has published regulations relating to the use of cobalt driers and methyl ethyl ketoxime. See Miljoprojekt, 884 2003. “Substitution of Cobalt driers and methyl ethyl ketoxime” at 6 Environ, Pages 1-12. However, it does not appear likely that all oximes will be restricted by REACH or similar regulations.
Another oxime, cyclohexanone oxime, has been used as an anti-skinning agent in relatively few applications. This is apparently due to the fact that cyclohexanone oxime is somewhat difficult to handle in pure form. Pure cyclohexanone oxime is a crystalline solid and subject to sintering at room temperature. Significant time and mixing energy is required to dissolve pure cyclohexanone oxime in liquid coating materials. In other respects, cyclohexanone oxime is an attractive candidate for use as an anti-skinning agent in oil-based coating materials.
Delivering a more concentrated cyclohexanone oxime solution, rather than a less concentrated cyclohexanone oxime solution, tends to reduce shipping costs and storage costs. For example, the savings associated with shipping and storing solutions including 20 mass percent cyclohexanone oxime or more are significant. Consequently, manufacturers of oil-based coating materials would welcome a delivery solvent that permits relatively concentrated cyclohexanone oxime solutions to be efficiently shipped, stored and employed with their products.
The solubility of cyclohexanone oxime in previously known delivery solvents is limited. Also, for safety reasons, solutions having relatively high flash point temperatures and relatively less Volatile Organic Carbon content (“VOC content”) are favored by the industry. Even then, not all of the previously known solvents are compatible with use in oil based coating materials.
The stability and compatibility requirements associated with manufacturing oil-based paints are representative of requirements posed by the oil-based coatings industry in general. Oil-based paints typically contain unsaturated resins dissolved or dispersed in an organic medium that are intended to form a solid film on a substrate. These resins are initially present in the coating composition as liquids, or as particles dispersed in a liquid phase. Once the coating composition has been applied to a substrate, a polymerization reaction chemically converts the unsaturated resin into the solid film. The polymerization reaction is often called “drying”, even when it is not associated with a loss of water. The polymerization reaction may be initiated by, for example, exposure to oxygen present in the surrounding atmosphere or radiant energy such as ultraviolet light. The mechanisms involved are described in a technical paper by K. U. Ingold entitled “Inhibition of the autoxidation of organic substances in the liquid phase”, which was published Feb. 1, 1961 by the Division of Applied Chemistry, National Research Council, Ottawa, Ontario, Canada.
Alkyd resins are the dominant binder in many commercial paints and other oil-based coatings. Alkyd resins are produced by the reaction of polyols with carboxylic acids or anhydrides. To make them susceptible to the drying process, and to impart of a degree of flexibility to the resulting dry film, some alkyd resins are reacted with unsaturated triglycerides. Plant and vegetable oils, such as tung oil and linseed oil, are frequently the source of the triglycerides. In these drying alkyds, unsaturated alkene groups can react with oxygen from the air, causing the oils to crosslink, harden, and appear to dry. The length of time required for drying depends on the amount and type of drying oil employed, and the presence of organic metal salts, also known as “driers”, which catalyze polymerization of the unsaturated oils.
The driers for oil-based coatings generally catalyze oxidative radical cross-linking of the oils to form three-dimensional polymer networks. Successful driers for oil-based coatings frequently include carboxylates of metals such as cobalt, magnesium, manganese, lead, zirconium, zinc, vanadium, calcium and iron. The carboxylate portion of the driers can be derived from, for example, 2-ethyl hexanoic acid, isononanic acid, heptanoic acid, versatic acid and linseed oil fatty acids. Driers commercially available from Troy Chemical Corporation of Florham Park, N.J. under the registered tradenames Troychem® or Troymax® exemplify these metal carboxylate driers.
Anti-skinning agents are frequently employed with driers in oil-based coatings to prevent skinning or lumpy material formation in the coating material during transportation and storage. In a typical manufacturing process for oil-based coatings, an anti-skinning agent, a drier, an oil-based solvent and, optionally, a pigment and well-known adjuvants are blended with a drying alkyd resin and stirred at a temperature below the fusion temperature of the alkyd resin. The resulting coating material is subsequently placed in a can, drum, tank, or other container for storage and/or transportation. The period of storage and/or shipment may last several months or more. As the containers are not generally temperature-controlled, their contents may be exposed to temperatures ranging from −8 to about 30 degrees C.
Solvents employed in the manufacture of cyclohexanone oxime reportedly include water; alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol and tert-amyl alcohol; nitriles, such as acetonitrile and propionitrile; aliphatic hydrocarbons, such as n-hexane and cyclohexane; aromatic compounds, such as benzene and toluene; and ethers, such as dioxane and diglyme; and water. While these solvents may be satisfactory for manufacturing purposes, many of them have undesirably low flash point temperatures. For whatever reason, it appears that only relatively dilute solutions of cyclohexanone oxime are presently being employed as cyclohexanone oxime delivery systems for use in oil-based coating materials.
A commercially practical cyclohexanone oxime concentrate would include at least about 20 mass percent cyclohexanone oxime as a solute dissolved in a clear solution at room temperature. If the commercially practical cyclohexanone oxime concentrate exhibits any precipitation, phase separation or clouding as a result of temperatures encountered during storage or transportation, the concentrate should recover its original appearance upon return to room temperature.
A desirable cyclohexanone oxime concentrate would exhibit relatively high flash point temperature and a relatively low VOC content. Preferably, the cyclohexanone oxime concentrate will have a flash point temperature of 45 degrees C. or more. Ideally, the flash point of the cyclohexanone oxime concentrate will have a flash point temperature of 60 degrees C., in order to satisfy transportation safety standards in Europe, Canada and the United States.
Accordingly, a need exists for a solvent or system of co-solvents which can be employed for storing and delivering a relatively concentrated solution of cyclohexanone oxime to manufacturers of oil-based coating materials. The ideal solvent may subsequently perform a beneficial role in the manufacturing process. At a minimum, the solvent should remain stable throughout the coating material and should not detract from the quality of the finished coating material.